Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $58.86   6.318%   $62.5788   $62.58   $62.60   $62.60  
  Purchase #2 $219.42   11.148%   $243.8809   $243.88   $243.90   $243.90  
  Purchase #3 $183.54   8.430%   $199.0124   $199.01   $199.00   $199.00  
  Purchase #4 $157.96   12.704%   $178.0272   $178.03   $178.05   $178.00  
  Purchase #5 $107.45   4.225%   $111.9898   $111.99   $112.00   $112.00  
  Purchase #6 $123.33   9.523%   $135.0747   $135.07   $135.05   $135.10  
  Purchase #7 $234.30   11.389%   $260.9844   $260.98   $261.00   $261.00  
  7 purchase totals = $1,084.86       $1,191.5482   $1,191.54   $1,191.60   $1,191.60